Yes, you read that correctly.
The stuff we flush down the toilet every day could eventually become part of the answer to one of net zero’s toughest problems: how the hell do we decarbonise aviation without giving up flying?
This week on the Net Hero Podcast I spoke to James Hygate, CEO of Firefly Green Fuels, who has spent decades working with biofuels and is now trying to turn sewage waste into sustainable aviation fuel.
His journey actually began in his parents’ garage in Stroud.
“I read a little bit about making biofuel. I grew up in a place called Stroud in Gloucestershire, which is quite alternative, so it was completely normal for someone to go and build a small biorefinery in their parents’ garage, which is what I did to power my own vehicle.”
That experiment eventually became Green Fuels, which James says grew into the world’s largest supplier of biofuel technology. But he realised energy-dense liquid fuels would ultimately be most valuable in sectors that are incredibly difficult to electrify.
Aviation was the obvious target.
The breakthrough came when his team started looking at biosolids – the material left behind at the end of wastewater treatment.
“There’s loads of this stuff. We make it every day, multiple times a day! Its current disposal route is disappearing, so we’re like, this is a great opportunity. The challenge is that it’s wet, but we’d already started to look at how you deal with these wet materials.”
The clever bit is something called hydrothermal liquefaction, which James describes much more simply as a “fancy pressure cooker.”
“You put this material to high pressure. The water becomes quite interesting at that point and provides the environment and acts as a reagent in the reaction to form a biocrude and a biochar. Once you’ve got that biocrude, it’s like a fresh fossil crude, and you can then refine that into fuels.”
So sewage becomes crude oil and crude oil becomes jet fuel.
But this only matters if the economics work and James is adamant they can.
“If you want to do this at scale, you’ve got to be cost competitive. That was our filter. We spent years and years testing everything and then when we found shit, basically, we were like, hey, this is the future.”
And biosolids could only be the beginning. Agricultural waste and other wet biomass could potentially follow.
“This is how you get your gigaton. You can’t do it just with biosolids. When you start moving it more broadly to other wet wastes, there is a light at the end of the tunnel here. There is actually a possibility to start utilising these materials.”
Firefly is targeting commercial-scale production by 2030, with qualified fuel actually going into aircraft.
And no, James assures me the plane won’t smell. ✈️💩
Would you fly on poo power? I would.
Listen to the full conversation with James Hygate on the Net Hero Podcast, download the episode wherever you get your podcasts and please subscribe.
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